In a conventional system including a solar power generating unit and an electricity storing unit, there is provided a method for effectively utilizing electricity generated by a solar power generating unit to reduce an amount of electricity purchased from a commercial power source. In JP-A-2003-309928, there is disclosed a method for activating or stopping an electricity using appliance as needed on the basis of an amount of electricity generated by a solar power generating unit and an amount of electricity supplied from an electricity storing unit, and an amount of electricity used by the electricity using appliance.
In a technology described in this JP-A-2003-309928, there is a case where the electricity using appliance is stopped in order to reduce the amount of the electricity used by the electricity using appliance. In this case, although a user wants to use the electricity using appliance, the electricity using appliance is forcibly stopped, so to speak, which presents a problem of inconvenience.
In contrast to this, in JP-A-2007-295680, there is disclosed a technology of predicting an amount of electricity generated by a solar power generating unit and an amount of electricity consumed to thereby increase an amount of electricity used late at night.
In the technology described in this JP-A-2007-295680, there is a case where because an amount of electricity to be sold (an amount of surplus electricity flowing reversely to a power system) needs to be increased, the use of an electricity using appliance is limited in order to efficiently operate a power conditioner of the solar power generating unit. When the amount of surplus electricity flowing reversely to a power system is given higher priority, it may not be clear whether all of the electricity flowing reversely to the power system is consumed by the other building or is not consumed but is lost due to a transmission resistance. In other words, when the amount of surplus electricity flowing reversely to a power system is increased, solar electricity may not be effectively used.